When head-to-disc contact vibration causes a head to align with a wrong track on a disc, data can be written on the wrong track, overwriting data that is lost. A channel is needed that can sense head-to-disc vibration quickly so that write current can be shut off, however, it is difficult to quickly sense head-to-disc contact vibration with adequate signal to noise ratio when there is a background vibration noise spectrum present that is produced by a pulse drive to a disc motor. The vibration noise spectrum is found to have local noise maxima that interfere with sensing head-to-disc contact vibrations.
Aspects of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.